Powder sprayer with flexible blades



Sept. 12, 1967 w. G. EBUHLER BLADES POINTER SPRAYER WITH FLEXIBLE 6Sheets-$heet 1 Filed Aug. .1966

R O T m W A A WAIAW'MN 4:55. SUM; ER

Sept. 12, 1967 w. G. BUHLER POWDER SPHAYER WITH FLEXIBLE BLJADES 6Sheets-Sheet 2 Filed Aug. 15, 1966 INVENTOR.

WARREN G- BUHL ER A T TOR NEYS P 1967 w. G. BUHLER I 3,341,740

POWDER SPRAYER WITH FLEXIBLE BLADES Filed Aug. 15, 1966 6 Sheets-SheetI! I P N r L Aza- ()7 IN VEN TOR. WARREN a. BUI-I -ER A TTORNEYS Se t12, 1%? w. s. BUHLER FC'WDEFI SfR/WLJR WITH lI/EXIBLF BLADES 6Sheets-Sheet Filed Aug. 15 1966 .1 NV EN TOR. WA @WWEN (3 123' UN 1 A???w FHNH 5111 i v n W n WI M MH Sept. 12, 1967 w. G. BUHLER POWDER SPRAYERWITH FLEXIBLE BLADES 'Filed Aug. 15, 1966 6 Sheets-Sheet 5 F/G. l0

fio w o Q d 0 0 0 0 INVENTOR. WARREN G. BUI-ILER A rromvevs Sept. 12,1967 w. G BUHLER POWDER SPRAYER WITH FLEXIBLE BLADES Filed Aug. 15, 19666 Sheets-Sheet G1 1 I I I I r 1 I 1 1 I I I INVENTORJ W WARREN G. BUHLERTTORNEYS United States Patent Office 3,341,740 Patented Sept. 12, 19673,341,740 POWDER SPRAYER WITH FLEXIBLE BLADES Warren G. Buhler,Westfield, N.J., assignor to Oxy-Dry Sprayer Corporation, New York,N.Y., a corporation of New York Filed Aug. 15, 1966, Ser. No. 572,542 4Claims. (Cl. 317-2) ABSTRACT OF THE DISCLOSURE chamber.

This invention relates to powder sprayers, and more particularly, topowder sprayer units capable of laying down a substantially uniformlayer of fine particle material upon a surface which is usually in theform of a moving web or sheet.

The prior electrostatic powder sprayers have usually included a powderbox, a metering mechanism for dispensing the powder material at auniform rate, and apparatus which provides an electrostatic field tofree the powder particles from the metering mechanism and to dispersethe particles so that they fall by gravity to the surface belowproviding a uniform powder layer. The metering mechanism usuallycomprises a dispensing roller and a tangential wiping blade. Typically,this tangential wiping blade is fairly rigid and relatively wide so thatit can be disposed within the powder box and, in addition to performingthe metering function, also provide an unobstructed sloping surface forfunneling the powder toward the dispensing roller.

Although reasonable success has been achieved, there are neverthelessseveral disadvantages inherent in the prior structures. As a practicalmatter, it is virtually impossible to construct a perfectly straightwiping blade due to the molecular structure and setress patterns in theblade material. In order to obtain a reasonably straight blade, theblade would be creased longitudinally during fabrication. Thereafter,when the blade is installed, it is necessary to overcompensate byincreasing the blade pressure against the roller sufficiently to insurethat the wiping blade engages the dispensing roller throughout itsentire length. The increased blade pressure increases the requireddriving torque for the roller and as a result requires a larger drivingmechanism. Since the blade pressure cannot be controlled accuratelythroughout the length of the blade, variations in blade pressure couldnot effectively be used as a means for varying the powder dispensingrate. Also, it was very difiicult to operate with relatively high rollerspeeds since it was diflicult to maintain adequate blade pressure at allpoints along the roller engaging blade surface.

The fact that the wiping blades are pre-bent also creates a problemsince it is necessary to carefully package the blades in rigidcontainers after fabrication so that the blades are not bent out ofshape during storage and shipping. As a result, the packaging, storingand shipping expenses were substantial. The pre-bent rigid wiping bladeswere also found difiicult to install on location and not readilyadjustable to compensate for tolerances in the supporting structure oruneven wear. Furthermore, the fact that the wiping blades were disposedinside the powder box created numerous problems when attempting toreplace a worn out blade.

An object of this invention is to provide a powder sprayer including awiping blade arrangement which overcomes the disadvantages experiencedwith prior structures.

An other object is to provide a powder sprayer utilizing flexible wipingblades which are not pre-bent and which can therefore be rolled up whennot in use to facilitate storing and handling and substantially reducethe required manufacturing accuracies.

Another object is to provide powder sprayers wherein the wiping bladesare secured to the outside of the powder box so that the blades caneasily be replaced without disassembling the sprayer unit or removingthe sprayer unit from its normal installed position.

Another object is to provide a powder sprayer utilizing relativelynarrow wiping blades which are easily adjustable to provide the desiredblade pressure against the dispensing roller so that friction betweenthe roller and the blade can be minmimized and so that the propermetering action can be achieved throughout a relatively wide range ofroller speeds.

Another object is to provide a powder sprayer wherein the wiping bladeis easily adjustable with respect to the dispensing roller so that thepressure against the roller can be varied as desired to compensate fortolerances in the supporting structures and inaccuracies due to unevenwear.

Another object is to provide a powder sprayer wherein the wiping bladesare easily adjustable to control the dis pensing rate and to attaincertain controlled uneven powder distribution when desired.

In addition to the powder box, dispensing roller, wiping blades, andelectrostatic field generating apparatus, powder sprayers usuallyinclude a pneumatic structure for creating an air curtain on each sideof the sprayer between the powder box and the surface below receivingthe powder layer. This air curtain confines the powder material to thearea below the roller and eliminates the eifect of ambient air currents.

A further object of the invention i to provide an integral structurewhich both supports the wiping blades and provides an air curtain.

A still further object is to provide a pneumatic structure for creatinga relatively uniform air curtain, which is located within the powder boxbut does not decrease the useful capacity of the powder box.

Another object is to provide a pneumatic structure having a relativelylarge plenum chamber which creates an air curtain which is substantiallyuniform over the entire length of the powder sprayer.

Still another object is to provide a pneumatic structure which providesa substantially uniform air curtain and which also prevents accumulationof powder on external portions of the sprayer unit.

The manner in which the foregoing and other objects are achived is setforth more fully in the following specification which describes a fewillustrative embodiments within the scope of this invention. Thedrawings form a part of this specification wherein:

FIG. 1 is a perspective view, with portions broken away, illustratingone end of the powder sprayer;

FIG. 2 is a perspective view illustrating the other end of the powdersprayer with the journal structure partially disassembled;

FIG. 3 is a plan view of the powder sprayer and associated drivingmechanism;

FIG. 4 is a side view of the powder sprayer;

FIG. 5 is an end view of the powder sprayer taken along line 55 asindicated in FIG. 4;

FIG. 6 is a cross sectional view of the powder sprayer taken along line6-6 as indicated in FIG. 4;

FIG. 7 is a longitudinal cross sectional view of the powder sprayerillustrating the journal structure and taken along line 7-7 as indicatedin FIG. 3;

FIG. 8 is an enlarged partial cross sectional view of the structureshown in FIG. 6 illustrating the details of the wiping blade assembly;

FIG. 9 is an illustration of the roller surface in accordance with oneembodiment of the invention as seen from line 99 in FIG. 8;

FIG. 10 is an illustration of an alternative surface structure for theroller as seen along line 99 in FIG. 8;

FIG. 11 is a cross sectional view illustrating the socket structure forretaining one end of a discharge tube;

FIGS. 12 and 13 are cross sectional views of one of the end bracketstaken along line 1212 in FIG. 4 and illustrating the adjustabledischarge tube support structure.

GENERAL DESCRIPTION The side panels for the powder sprayer in accordancewith this invention are constructed having sloping inner surfaces whichlie in planes generally tangential to the dispensing roller so that allof the powder or dusting materials within the powder box is funneledtoward the roller. The outer surface of a side panel is vertical so thata triangular cavity is formed within the panel to provide a plenumchamber. A longitudinal V-shaped groove is machined into the lowerhorizontal portion of the side panel between the sloping and verticalsurfaces. A plurality of holes are spaced along this groove so that whenair pressure exists within the plenum chamber a large number of air jetsare provided along the groove. Due to the groove, the jets fan outelliptically and inwardly to thereby provide a relatively uniform aircurtain. The inwardly direction portion of these jets preventaccumulation of powder on the external surfaces of the wiper blade andassociated supporting structure.

The wiping blade is relatively narrow and is constructed from arelatively thin strip of blue spring steel. Preferably, the wiping bladeis coated with a fluro-carbon material. Thus, the wiping blade isflexible and therefore can easily be rolled up during storage andshipping.

The inwardly slanted surface of a side panel extends below the plenumchamber. This extended portion of the side panel is shaped to provide aretaining surface for the wiping blade. The wiping blade is securedbetween the retaining surface and a retaining strip by means oflongitudinally spaced adjusting screws. The retaining strip is shaped soas to deform the flexible wiping blade transversely of the roller overthe entire length of the blade or in other words, so that the wipingblade will take on a transverse S-shaped bend extending from one end ofthe blade to the other. As a result of this bend, the wiping bladebecomes relatively rigid and substantially straight in the longitudinaldirection. Since the blade is flexible, relatively narrow, and thesecuring structure is relatively close to the dispensing roller, theblade pressure against the roller can be accurately controlled by meansof the adjusting screws.

POWDER BOX, WIPER BLADES AND AIR CURTAIN formed as an integral portionof the end brackets. The

side panels are secured to the support blocks by means of suitablescrews as illustrated. A spacer member 12 is secured intermediate theends of the side panels and is flush with the upper edge thereof. A lid6 is secured to the upper edge of side panel 2 by mean of a hinge 9 andis dimensioned to cover the top of the powder box and wrap over theupper edge of side panel 3 when in the closed position. Dispensingroller 11 is journaled in the end brackets and is disposed between thelower edges of side panels 2 and 3.

The side panels, best seen in FIGS. 1, 6 and 8, are preferably integralextruded aluminum panels. Side panel 3 includes a vertical outer portion14, a sloping portion 15 and a lower horizontal portion 16, whichportions define a plenum chamber 17 having a generally triangular crosssection and extending through the side panel from end to end. Thesloping surface 15 lies in a plane tangential to dispensing roller 11and meets vertical portion 13 somewhat below the upper edge of the sidepanel. Surface 15 extends beyond the horizontal portion 16 and forms onesurface of a lower extended portion 18. The other flat surface ofextended portion 18 is blade retaining surface 19 which lies in a planewhich meets the plane of surface 15 at the point of tangency with theroller, or somewhat below the point of tangency. The right dihedralangle between these planes is approximately 20 degrees. The lower edgeof extended portion 18 is rounded as shown.

A longitudinal V-shaped groove 25, best seen in FIG. 8, is machined intothe lower surface of horizontal portion 16. This groove forms an outervertical groove surface 26 and inwardly sloping groove surface 27.Preferably, the groove is located directly below the outer portion ofplenum chamber 17. A plurality of holes 28 are drilled through bottomportion 16 extending between the apex of groove 25 and plenum chamber 17When the side panel is secured in position, the bracket 4 seals off oneend of plenum chamber 17, and end bracket 5 seals off the other end.Preferably, a sealing gasket is connected in position between the endbrackets and the side panels. A hose connecting nipple 29 is threadedinto a threaded bore 30 passing through end bracket 4 so as tocommunicate with plenum chamber 17. A suitable air pump can be coupledto the plenum chamber via an air hose (not shown) to create a pneumaticpressure within the chamber. As a result, a plurality of air jets areformed via holes 28. Because of groove 25, these jets tend to fan outelliptically and thus provide a relatively uniform air curtain extendingbetween adjacent holes throughout the entire length of the side panel.Due to sloping groove surface 27, a portion of each of these jets isdirected inwardly to prevent accumulation of powder on retaining member20, adjusting screws 22 and wiping blade 23 located beneath the sidepanel.

Side panel 2 is identical to side panel 3 and includes components 33-49corresponding, respectively, to components 13-29 of side panel 3. Asshown in FIG. 6, the powder material to be dispensed is placed in thepowder box between sloping surfaces 15 and 35 and above dispensingroller 11. Thus, the sloping surfaces serve to funnel the powderdownwardly toward the dispensing roller. It should be noted that theplenum chambers are therefore located in an area which would otherwisebe wasted space. Plenum'chambers 17 and 37 are sufliciently large sothat the air pressure therein is substantially uniform over the entirelength of the side panels.

Wiping blades 23 and 43 are each constructed from a thin, flexible stripof blue spring steel and are preferably coated with a fluro-carbonmaterial. These blades are ap proximately one inch wide and have alength equal to the length of side panels 2 and 3. Holes are drilledthrough the blade near the upper edge and are spaced on two inchcenters.

Semi-rigid retaining member 20, best seen in FIG. 8, is preferably anextruded aluminum strip equal in length to wiping blade 23 and sidepanel 3. Longitudinally spaced holes are drilled through retainingmember 20 corresponding in position to the holes in blade 23, andcorresponding tapped holes are drilled into extended portion 18 of sidepanel 3, these holes being normal to blade retaining surface 19. Wipingblade 23 is positioned between extended portion 18 of the side panel andretaining member 20, and this assembly is secured by means of suitableround head adjusting screws 22. Preferably, the holes in the wipingblade, retaining member and extended portion of the side panel areaccurately aligned so that the wiping blade can easily be replaced.

Retaining member 20 includes a flat blade engaging surface which curvesinto an inwardly etxending rib 21 at the lower edge thereof. Thedistance between screw 22 and rib 21 must be greater than the distancebetween screw 22 and the lower edge of extended portion 18. The distancebetween screw 22 and the upper edge 24 of the retaining member ispreferably somewhat greater than the distance along surface 19 betweenscrew 22 and the lower surface of bottom portion 16. Thus, when screw 22is tightened, moving retaining member 20 toward retaining surface 19,the upper edge 24 strike the lower surface of bottom portion 16.Thereafter, when screw 22 is further tightened, retaining member 24pivots about edge 24 and applies pressure along the longitudinal centerline of blade 23 via rib 21. As a result, the blade is bent inwardly byrib 21 along the center line of the wiping blade which is locatedbetween extended portion 18 and line of tangency on roller 11. Thus, thewiping blade is laterally deformed and takes on an S-shaped bend asshown in FIG. 8. In this manner, the flexible blade becomes rigid andsubstantially straight in the longitudinal direction. Each of the screws22 are separately adjustable, and hence, the pressure applied by thewiping blade against dispensing roller 11 can be adjusted as desired atselected points along the blade. This permits adjustments to compensatefor uneven wear or for tolerances in the dispensing roller surface orthe side panel. Also, it is possible to adjust the blade so that greaterpressure is exerted against the dispensing roller in selected areas tothereby obtain a non-uniform dispensing rate when desired.

END BRACKETS AND DISCHARGE TUBE MOUNTING STRUCTURE End brackets 4 and 5are identical to one another and are secured abutting the ends of sidepanels 2 and 3 by means of support blocks 9 and respectively which formintegral portions of the end brackets. The end brackets. The endbrackets thus serve as closure members for the ends of the powder boxand the ends of the plenum chambers within the side panels. Also, theend brackets support bearings for the journals for dispensing roller 11,arcuate surfaces for cooperating with the discharge tube supportingstructure, and bracket portions for securing the powder sprayer toassociated apparatus or a suitable support frame structure.

End bracket 4 is an integral structure including an end closure member60, a substantial circular boss 61 extending horizontally away from thesurface of closure member, and a support leg 62 extending horizontallyfrom the flat surface of the boss. The diameter of circular boss 61 isapproximately equal to the distance between the outer surfaces of sidewalls 2 and 3. Boss 61 is positioned to accommodate an off-centerjournal housing 53 for discharge roller 11, the discharge roller beinglocated as shown in FIG. 12. The lower portion of closure member 60,i.e., the portion lying below the horizontal center line of boss 61, iscurved and conforms to the circular configuration of the boss. Supportblocks 9 are secured to the edges of closure member 60 and extend in thedirection of the side panels. Support blocks 9 are spaced apart so thatthey will lie on the outer surfaces of the side panels when the endbracket is secured in position. The upper edges of closure member 60 andboss 61 6 are flush with the upper edges of side panels 2 and 3.

Support leg 62 can have any desired configuration and includes a pair ofslots 64 and 65 therein extending through the support leg from top tobottom. As shown in FIG. 7, support leg 62 is positioned slightly belowthe upper surface of boss 61 and is strengthened by means of a taperedrib 66 extending from boss 61 along the upper surface of the supportleg. The support leg can be either horizontal as shown, or can bevertical to facilitate side mounting.

End support bracket 5 is an integral structure identical to end supportbracket 4 and includes an end closure member 70, a substantiallycircular boss 71, a pair of spaced-apart support blocks 10, and asupport leg 72 with an asociated strengthening rib 76 and slots 74 and75. Thus, when the end brackets are secured in the positions as shown inFIGS. 1 and 2, the brackets close the ends of the powder box and alsoclose the ends of the plenum chambers within the side panels.Preferably, a sealing gasket is cemented in position between the endbrackets and the ends of the side panels. As previously mentioned, apair of bores 30 and 50 are provided extending through end bracket 4 andare each positioned to communicate with a different one of the plenumchambers 17 and 37 respectively. The threaded bores are adapted toaccommodate threaded hose connecting nipples 29 and 39 respectively. Endbracket 5 likewise includes a pair of threaded bores so that this endbracket will be identical to end bracket 4. The threaded bores in endbracket 5, however, are not used and are therefore sealed by means ofsuitable threaded plugs 77 and 7 8. The assembled powder sprayer can bepositioned as de sired by means of suitable bracket members (not shown)bolted to support legs 62 and 72 or by bolting the support legs directlyto a suitable supporting structure.

Discharge tubes 80 and 81 are similarly constructed and each includes acylindrical glass tube which is evacuated and then filled with an inertgas such as argon. The glass tubes are slightly longer than the sidepanels and are internally coated with a suitable phosphorous material.The discharge tubes include a cathode at one end only. As shown in FIG.11, the cathode end of the discharge tube includes a cup shaped cathodemember 82 connected to a conductive metallic end cap 83 by means of asuitable support conductor 84.

It is desirable that the discharge tubes be positioned generallyparallel to dispensing roller 11 and that they be adjustable in positionwith respect to the roller. Also, it is desirable that the tubes bedetachably secured so that they can easily be replaced.

The discharge tube support structure for tube 81 includes a support armhaving an arcuate inner surface with the same radius of curvature as thearcuate surface 91 at the periphery of boss 61. Thus, the inner surfaceof support arm 90 is adapted to engage arcuate surface 91 as shown inFIG. 1, and is adjustable with respect to the boss. Support arm 90includes an elongated locking slot 92 including an elongated annularshoulder 93 (best seen in FIGS. 12 and 13) which is concentric with thearcuate surface of boss 61. A tapped hole is bored into boss 61 alongthe horizontal center line and is dimensioned to accommodate a sockettype cap screw 94 which passes through slot 92. Thus, when cap screw 94is loosely placed in position, support arm 90 can slide from an upperposition as shown in FIG. 12 to a lower position shown in FIG. 13. Itshould be noted that arcuate surface 91 is eccentric with respect to thedispensing roller surface due to the off-center location of the journalhousing with respect to boss 61. Support arm 90 can be rigidly secure atany position by tightening cap screw 94 so that the head of the screwengages shoulder 93 of the locking slot.

The lower portion of support arm 90 (as viewed in FIG. 1) is offset andis constructed to provide a bifurcated end portion 95 dimensioned toaccommodate a tab 96 extending from a spring biased tube socket 97. Asshown in FIG. 11, a pair of axially aligned threaded apertures passthrough the leg portions of bifurcated end 95 and a smalled diameter,axially aligned, aperture passes through tab 96. A pair of socket type,headless, set screws 98 and 99 are threaded into the leg portions ofbifurcated end 95 so that the dog point ends of the set screws residewithin the aperture passing through tab 96. In this manner, socket 97 ispivotably secured to support arm 90 (as illustrated in FIG. 13) and canbe rigidly maintained in any desired pivoted position by appropriateadjustment of set screws 98 and 99'.

A support arm 100, which is a mirror image of support arm 90, is adaptedto engage the arcuate surface 101 located at the periphery of boss 71 ofend bracket 5. Support arm 100 is secured to end bracket by means of acap screw 104 which passes through an elongated locking slot 102 andengages shoulder 103 within the slot. A tab 106 extending from acup'shaped tube socket 107 is pivotably secured to support arm 100 bymeans of an offset bifurcated end portion 105. Tube socket 107 ispreferably constructed from a material having a high electricalresistance and is dimensioned internally to accommodate then end ofelectrostatic tube 81.

Spring biased socket 97 includes a generally cylindrical outer housing110 which is partially closed at one end. An insulated conductor 111passes through the partially closed end of housing 110 and through thecenter of a retaining washer 1 12. The free end of the conductor isimbedded in a globule or head of solder 113 to provide a relativelylarge conductive surface and to prevent conductor 111 from pulling outof the washer. A spring 114 is disposed between retaining washer 112 andthe partially closed end portion of housing 110 to urge the retainingwasher away from the partially closed end of the housing. As previouslymentioned, tab 96, which extends radially from housing 110, is pivotablysecured by the bifurcated end portion of support arm 90. Housing 110 ispreferably an integral structure constructed from a material having ahigh electrical resistance.

Conductor 111 after emerging from the end of socket 97, is connected toone end of a high voltage secondary winding 115 of a transformer 116,the other end of the secondary winding being connected to a suitableground, which may be the side panels of the powder sprayer or a groundsurface located at some point below the sprayer. Primary winding 117 oftransformer 116 is connected to a suitable 60 cycle alternating currentsource. Transformer 116 is preferably constructed to provideapproximately 10,000 volts to electrode 82 via conductor 111.

Discharge tube 81 is installed by inserting the electrode end intospring biased socket 97 thereby compressing spring 114. The other end ofthe discharge tube is then inserted into socket 107, and when released,is retained in socket 107 by virtue of the force extended by spring 114.Thereafter, discharge tube 81 can easily be adjusted to any desiredposition parallel to dispensing roller 11 by means of the pivotableconnection between the sockets and support arms 90 and 100, or byadjusting the position of the support arms relative to end brackets 4and 5.

The adjustable support structure for discharge tube 80 is essentiallythe same as the supporting structure for discharge tube 81, except thatit is attached to position tube 80 on the opposite side of dispensingroller 11. The components comprising the adjustable supporting structurefor discharge tube 80 are designated with reference numerals 120-144corresponding respectively to reference numerals 90-114. Conductor 141emerging from socket 127 is also connected to the ungrounded end ofsecondary winding 115 (FIG. 11).

ROLLER ASSEMBLY Roller 11 can be a solid steel roller with longitudinalextending shafts as shown in the drawings, or can include a hollowcylindrical roller with suitable roller gudgeons secured to the ends toform the longitudinal extending shaft portions. The length of the rollerportion is slightly less than the distance between end brackets 4 and 5as determined by the length of the side panels.

Journal shaft 150, extending from one end of roller 11, passes through ajournal opening 151 in end bracket 5 forming part of journal housing 73,and through a flanged bearing 152 constructed from a suitable bearingmaterial, preferably a fiuro-carbon material. Journal opening 151 isdimensioned to accommodate flanged bearing 152 and includes an annularrecess dimensioned to seat the flange of the bearing. As shown in FIG.2, flanged bearing 152 is slid into position from outside end bracket 5and is thereafter secured to the end bracket by means of set screws 153passing through the flange of the bearing. An annular recess is alsoprovided on the inner side of end bracket 5 surrounding journal opening151, to accommodate a felt washer 154 which provides a journal seal andprevents powder from entering the hearing structure. A collar 155 isslid over the end of shaft 150 and is rigidly secured to the shaft bymeans of a set screw 156. This collar is positioned adjacent bearing 152and prevents longitudinal movement of the roller with respect to the endbracket. A sprocket gear 157 is secured near the end of shaft 150 bymeans of a suitable set screw passing through the hub of the gear. Asshown in FIG. 3, a chain 158 couples sprocket gear 157 to an associatedsprocket gear mounted on the shaft of an electric motor 159. Motor 159is preferably of a variable speed drive type capable of rotating roller11 at speeds ranging from small fractions of one rpm. to fifty r.p.rn.

Journal 63 in end bracket 4 is similar to journal 73 previouslydescribed and includes a flanged bearing 162 secured in a journalopening 161 by means of set screws 163 so that the bearing surroundsshaft extending longitudinally from the end of roller 11. A felt sealingwasher 164 is provided surrounding the shaft on the inner side of endbracket 4, and a collar 165 is secured to shaft 160 adjacent bearing 162by means of set screw 166.

The cylindrical surface of roller 11 is advantageously coated with afluro-carbon material and thereafter further processed to provide apowder receptive surface. The processed surface of the roller isillustrated in a magnified view of the roller surface shown in FIG.' 9and includes an almost infinite number of small powder carryingcavities. As illustrated in FIG. 8, the powder material in powder box 1is fed by gravity into the area between roller 11 and wiping blade 23.As the roller rotates, a thin layer of powder wedges passed the wipingblade. The thickness of the powder layer, and hence, the quantity ofpowder dispensed, depends on the adjustment of screws 22 which in turndetermines the blade pressure against the roller. The minimum rate atwhich powder can be dispensed is determined by the capacity of thepowder carrying cavities and the minimum rotation speed of thedispensing roller. The dispensing rate can be increased by eitherincreasing the rotation speed of the roller or by decreasing the bladepressure against the surface of the dispensing roller.

An alternative surface structure for the dispensing roller isillustrated in FIG. 10 where the cylindrical surface is engraved topresent a uniform waffle-like pattern. This structure increases thecapacity of the powder carrying cavities which is desirable where highdispensing rates are required or large powder particles are beingdispensed. Preferably, the engraved dispensing roller is coated with afluro-car-bon material. With the dispensing roller surface shown in FIG.10, the dispensing rate can also be varied by adjusting the speed ofrotation for the dispensing roller and the wiping blade pressure.

Although it has been mentioned that the dispensing rate for a givenroller surface can be adjusted by varying the roller speed and bladepressure, there is a practical limit to these adjustments sinceeventually the powder will begin to sift, that is, the powder will beginto come through in uneven chunks resulting in an uneven and relativelyuncontrolled powder distribution. The maximum dispensing rate for aparticular roller varies in accordance with the type of powder beingdispensed. When a particular roller does not achieve the desireddispensing rate, the roller is replaced with another roller having largepowder carrying cavities.

It is significant that the roller and the wiping blades are coated witha fluorocarbon material and that the roller bearings are likewiseconstructed from a fluorocarbon material. The fluorocarbon material usedfor coating the roller and wiping blades is preferably the polymer oftrifluorochlorethylene characterized by the formula (CF CFCl) First,these materials exhibit a high chemical resistance so that othermaterials, such as the powder being dispensed, cannot readily adhere tothe roller and wiping blade surfaces. Second, fluorocarbon materialshave substantially a zero moisture absorption characteristic andtherefore reduce the possibility of moisture contamination of the powderbeing dispensed. Third, these materials have a relatively highcompression strength and hence, excellent wear characteristics. This issignificant in the bearings, and also With respect to the roller andwiping blade arrangement which is subjected to the constant rubbingaction as the powder material, which may be abrasive, passes between theroller and Wiping blade. Further, fluorocarbon materials have a highelectric resistance and high resistance to electrostatic charges. Itshould be noted that the steel roller, due to the flanged fluorocarbonbearing and fluorocarbon coating is electrically isolated and hence, iselectrically insulated from the electrostatic field. If the dispensingroller were not isolated, there would be some electric charge, from theelectrostatic field created by discharge tubes 80 and 81, which would becarried into the powder box by means of the roller and therebyelectrostatically contaminate the powder material. This electrostaticcontamination would adversely effect the dispensing of the powdermaterial.

ASSEMBLY AND OPERATION The powder sprayer in accordance with thisinvention is of a generally symmetrical design so as to minimize thenumber of different components. The side panel and wiping blade assemblyon one side of the roller is identical to the side panel and wipingblade assembly on the other side. The end brackets are identical to oneanother, and the two discharge tubes supporting structures are alsosubstantially identical. This symmetrical construction is alsoadvantageous since the dispensing roller can be rotated in eitherdirection and the entire unit can be installed with either side panelfacing outwardly.

The powder sprayer is installed with the dispensing roller postionedhorizontally, usually less than a foot above the surface to be coatedwith the powder material. Usually, the powder receiving surface is inthe form of a moving web or sheet.

The powder or dusting material to be dispensed is either placed directlyin the powder box above dispensing roller 11 or is supplied by asuitable feed mechanism. Thereafter, the drive motor is energized torotate motor 11. The roller, if rotating in a clockwise direction,forces powder past wiping blade 23, in which case wiping blade 43 actsas a seal between the side panel and the other side of the roller. Onthe other hand, if the dispensing roller rotates in a counterclockwisedirection, wiping blade 43 provides the metering function and wipingblade 23 acts as the seal. In either event, the powder material ismetered out at a uniform rate. Thereafter, the force of gravity and theforce created by the electrostatic field provided by the dischargetubes, strips the roller clean so that the powder material falls to thesurface below.

When discharge tubes 80 and 81 are energized, potential gradients arecreated surrounding the tubes which in turn ionize some of the airmolecules in the vicinity of the discharge tube. This effect is known ascorona. The ionized particles having the same polarity as that appearingin the surface of the discharge tube stream away from the dischargetubes creating air currents referred to as electronic winds. Theseelectronic winds are in a generally downward direction in the areabeneath dispensing roller 11. The downwardly directed electronic windand the electrostatic attraction of the powder particles assist theforces of gravity in removing the particles from the roller. A largenumber of the released particles become charged with the same polarityas the surrounding air molecules. This effect creates a powder cloudbeneath the dispensing roller and brings about a more uniform dispersionof powder particles than could otherwise be achieved.

As previously mentioned, the dispensing rate is determined by therotational speed of dispensing roller 11, and the blade pressure againstthe dispensing roller surface. It should be noted that the wiping bladeis relatively narrow and that the retaining member, which controls theblade pressure, is relatively close to the dispensing roller. With thisarrangement the blade pressure can be controlled with considerableaccuracy. Furthermore, since the adjusting screws are individuallyadjustable, the blade pressure can be adjusted separately in differentselected areas.

After the powder sprayer unit is placed in operation, the powderdistribution is observed and the roller speed and blade pressure areadjusted until a desired dispensing rate is achieved. If the powderdistribution is uneven, as may be caused by inaccuracies in thedispensing roller or side panels or by uneven wear, this is easilycorrected by adjusting the blade pressure in appropriate selected areas.In cases Where a particular uneven distribution is desired, for example,more powder in the center than at the ends, such uneven distribution canbe attained by adjusting the blade pressure so that it is greater at theends than at the center.

The position of the discharge tubes can be adjusted so that one or bothof the tubes are effective, and hence, the effective strength of theelectrostatic field can be varied over a relatively wide range. Also,the tube position can be adjusted to provide an electrostatic fieldwhich is nonsymmetrical and which thus tends to propel powder partidesin other than a directly downward direction. The non-symmetrical fieldcan be used, for example, to compensate for the effect of ambient aircurtains on the powder particles as they fall from the dispensing rollerto the surface below.

When the unit is placed in operation, a pneumatic pressure is created inthe plenum chambers by means of a suitable air pump to thereby create anair curtain on each side of the roller. These air curtains extendbetween the side panels and the surface below and thereby protect theenclosed area from ambient air currents.

Although only a few illustrative embodiments of the invention have beendescribed in detail, it should be obvious to persons skilled in the artthat there are numerous additional variations and embodiments within thescope of this invention. The invention is more particularly defined inthe appended claims.

What is claimed is:

1. In an electrostatic powder sprayer, the combination of a pair ofspaced apart end members;

means located between said end members defining a receptacle for powdermaterials;

a metering mechanism communicating with said receptacle for dispensingthe powder material at a substantially uniform rate, including acylindrical dispensing roller journaled between said end members withinan opening beneath said receptacle, and

at least one wiping blade tangentially engaging said roller;

means secured to said receptacle defining a plenum chamber,

a plurality of downwardly directed, jet forming apertures eachcommunicating with said plenum chamber, said apertures being disposedalong a line generally parallel to the aXis of said dispensing roller,and

a longitudinal groove communicating with the lower end of each of saidapertures so that jets formed by said apertures tend to spread in thedirection of said groove.

2. Apparatus in accordance with claim 1 wherein said groove includes asloping inner surface so that jets formed by fluid passing through saidapertures tend to spread inwardly toward said roller.

3. In a powder sprayer of the type including a dispensing roller andcooperating wiping blades arranged for dispensing powder material from apowder receptacle, the improvement comprising means secured to saidpowder sprayer and disposed to define a plenum chamber extendingparallel to the dispensing roller;

a longitudinal groove in said means along a lower surface thereof andextending parallel to the dispensing roller; and jet forming aperturesaligned along said groove and communicating with said plenum chamber.

4. Apparatus in accordance with claim 3 wherein said groove includes asloping inner surface so that jets formed by fluid passing through saidapertures tend to spread inwardly toward the dispensing roller.

References Cited UNITED STATES PATENTS MILTON O. HIRSHFIELD, PrimaryExaminer.

I. A. SILVERMAN, Assistant Examiner.

1. IN AN ELECTROSTATIC POWER SPRAYER, THE COMBINATION OF A PAIR OFSPACED APART END MEMBERS; MEANS LOCATED BETWEEN SIAD END MEMBERSDEFINING A RECEPTACLE FOR POWDER MATERIALS; A METERING MECHANISMCOMMUNICATING WITH SAID RECEPTACLE FOR DISPENSING THE POWDER MATERIAL ATA SUBSTANTIALLY UNIFORM RATE, INCLUDING A CYLINDRICAL DISPENSING ROLLERJOURNALED BETWEEN SAID END MEMBERS WITHIN AN OPENING BENEATH SAIDRECEPTACLE, AND AT LEAST ONE WIPING BLADE TANGENTIALLY ENGAGING SAIDROLLER; MEANS SECURED TO SAID RECEPTACLE DEFINING A PLENUM CHAMBER, APLURALITY OF DOWNWARDLY DIRECTED, JET FORMING APERTURES EACHCOMMUNICATING WITH SAID PLENUM CHAMBER, SAID APERTURES BEING DISPOSEDALONG A LINE GENERALLY PARALLEL TO THE AXIS OF SAID DISPENSING ROLLER,AND A LONGITUDINAL GROVE COMMUNICATING WITH THE LOWER END OF EACH OFSAID APERTURES SO THAT JETS FORMED BY SAID APERTURES TEND TO SPREAD INTHE DIRECTION OF SAID GROOVE.